Borescopes are commonly used for inspection of devices such as gas and steam turbine engines to determine if there are any cracks or defects in rotating components such as turbine blades. Existing borescopes are used to investigate internal parts of the devices for cracks or overall integrity of the parts without the need to open the device's cover. Existing borescopes include video borescopes that can capture video and/or still images of the parts. Video borescopes typically include a light that illuminates the parts to facilitate visualization of the video and/or still images. Different brightnesses of the light can be required in order to clearly visualize different parts of a turbine or other device. However, some borescopes do not allow brightness of the light to be varied at all.
One typical way that brightness of the light is controlled in some borescopes is by using pulse width modulation (PWM) in which a light in the form of an LED is repeatedly turned on and off, with the “on” versus “off” time determining the amount of brightness. However, the repeated on/off cycles of the light are detectable as visual artifacts on the video. The visual artifacts negatively affect user experience and reduce clarity and color accuracy of the video image. Another typical way that brightness of the light is controlled is by using an adjustable current source to supply power to a light in the form of an LED at a specific current. The current source typically measures a voltage across a current sensing shunt and compares an amplified version of the measured voltage to a reference voltage so as to set the specific current. However, the range in which the current source can be adjusted is typically narrow due to limitations in the range of the current sensing amplifier and due to limitations in reference voltage ranges. The LED can thus only provide brightnesses within a narrow range.
Accordingly, there remains a need for improved methods and devices for adjusting brightness of a light source.